An injection mould generally comprises two mould halves between which a mould cavity is defined. Sophisticated designs which are in particular used for injection moulding of disc shaped information carriers, such as DVD's, CD's and so on, are furthermore provided with a venting ring which can be moved around one of the moulds and delimits therein an annular boundary surface of the injection mould cavity. This ring is movable so as to reduce the volume of the injection mould cavity during injection moulding, the movable ring and the base plate being made of steel and at least one of the movable ring and the base plate being provided with a wear-resistant coating at the interface between said movable ring and the base plate.
An injection moulding mould part of this type is generally known in the state of the art. The distance between the venting ring and mirror must be particularly small if not zero in order to prevent plastic getting in-between. However, the venting ring must move with respect to the mirror or base plate during each opening and closing movement.
To prevent wear, it is proposed in the state of the art to provide either the base plate or the venting ring with a wear resistant coating. This wear resistant coating is a PVD (Physical Vapour Deposition) coating, such as a DLC (Diamond Like Carbon) coating.
It has been found that this coating is adequately wear-resistant, but that it cannot be guaranteed that the PVD coating, which is a few microns thick, will continue to adhere to the steel after prolonged use.
WO99/37471 A (assigned to patentee) discloses a mould assembly wherein a wear-resistant coating is used which is either coated with TiN or DLC. TiN has a hardness of about 2000–3000 HV, whilst the hardness of DLC is even higher.
JP 10008158 discloses the use of a functional film which will not crack and is applied by the HP-HVOF method. There is no indication about the use of such film.
JP 11-240624 discloses the use of a coating based on tungsten and cobalt in a dynamic condition.